ML20079Q106

Adequacy of Station Electric Distribution Sys Voltages, TMI Unit 1, Technical Evaluation Rept

ML20079Q106
Person / Time
Site:	Three Mile Island
Issue date:	12/31/1983
From:	Udy A EG&G, INC.
To:	Donohew J, Emami J Office of Nuclear Reactor Regulation
Shared Package
ML20079Q104	List: ML20079Q106
References
CON-FIN-A-6429 EGG-EA-6453, TAC-61740, NUDOCS 8401310524
Download: ML20079Q106 (16)

Text

- ________ __

. , EGG-EA-6453

, DECEMBER 1983 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES, THREE MILE ISLAND NUCLEAR STATION, UNIT 1 A. C. Udy Idaho National Engineering Laboratory Operated by the U.S. Department of Energy

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This is an informal report intended for use as a preliminary or working document 8401310524 840119 PDR ADOCK 05000289 P PDR Prepared for the U. S. NUCLEAR REGULATORY COMMISSION Under DOE Contract No. DE-AC07-761001570 II

- - E U R O ldaho FIN No. A6429 W  !

1 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES THREE MILE ISLAND NUCLEAR STATION-UNIT 1 A. C. Udy Published December 1983 EG&G Idaho, Inc.

Idaho Falls, Idaho 83415 Responsible NRC Individual and Division J. Emami/ Division of Systems Integration J. Donohew/ Division of Licensing Docket No. 50-289 TAC No. 61740 Prepared for the U.S. Nuclear Regulatory Commission Washington, DC 20555 Under DOE Contract No. DE-AC07-761001a?0 Fin. No. A6429

As A5STRACT This EG&G Idahe, Inc., report provides a review of the capacity and the capability of the onsite electrical distribution system at Unit No. 1 of the Three Mile Island Station, in conjunction with the offsite power sources, to automatically start and continuously operate all required safety loads.

FOREWORD This report is supplied as part of the " Selected Operating Reactors

, Issues Progrrm" being conducted for the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Licensing, by EG&G Idaho, Inc., NRC Licensing Support Section.

The U.S. Nuclear Regulatory Commission funded the work under the authorization, B&R 20 19 10 11.

NOTICE .

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employear, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, apparatus, product or process disclosed in this report or represents that its use by such third party would not infringe privately owned rights.

Docket No. 50-289 TAC No. 61740 11 s

• CONTENTS ABSTRACT ...................................................... ....... 11 FOREWORD .............................................................. 11

1. INTRODUCTION ..................................................... 1

2. DESIGN BASIS CRITERIA ............................................ 2

3. SYSTEM DESCRIPTION ............................................... 2 4 ANALYSIS DESCRIPTI23 ....... ..................................... 4 4.1 Design / Operation Changes ................................... 4 4.2 Ana ly s i s Condi ti on s . . . . . . . . . . . . . . s . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.3 An a l y s i s Re s ul t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.4 Analysis Verification ...................................... 6

5. E V A LU AT I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

6. CONCLUSIONS ...................................................... 10 l

7. REFERENCES ....................................................... 11 l

FIGURE

1. TMI-1 electric distribution ...................................... 3 TABLES

1. Class IE equipment voltage ratings and analyzed worst-case terminal voltages ................................................ 5

2. Comparison of analyzed voltages and undervoltage relay setpoints ........................................................ 9 iii

ADE0VACY OF STATION ELE'CTRIC DISTRIBUTION SYSTEM VOLTAGES THREE MILE ISLAND NUCLEAR STATION-UNIT 1

1. INTRODUCTION An event at the Arkansas Nuclear One Station on September 16, 1978, is described in NRC IE Information Notice No. 79-04. As a result of this event, station conformance to General Design Criteria (GDC) 17 is being questioned at all nuclear power s.,sionc. The NRC, in the generic letter of August 8, 1979, " Adequacy of Station Electric Distribution Systems Voltages,"I required each licensee to confirm, by analysis, the adequacy of the voltage to the Class IE loads. This letter included 13 specific guidelines to be followed in determining if the load terminal voltage is adequate to start and continuously operate the Class IE loads.

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In response to the NRC generic letter, the Metropolitan Edison

-Company, the licensee, submitted a voltage analysis on October 16, 1979.2 Because of determined voltage problems,_the licensee proposed design and procedural changes in their letter dated May 15, 1980.3 Also included was a voltage analysis based on these changes. Additional testing to confirm the voltage analysis was reported in a letter on Septemoer 30, 1983.4 Based on the information supplied by the licensee, this report incorporates a previous'EG&G Idaho, Inc., report.5 It addresses the capacity and capability of the onsite distribution system of the Three Mile Island Nuclear Station-Unit 1 (TMI-1), in conjunction with the offsite power system, to maintain the voltage for the required Class IE equipment within acceptable limits for the wor t-case starting and load conditions.

This report specifically updates Section 4.4 of the previous report, and related items in later sections, to include Reference 4.

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2. DESIGN' BASIS CRITERIA The positions applied in deterrining the acceptability of the offsite voltage conditions in supplying power to the Class IE equipment are derived

-from the following:

1. General Design Criterion 17 (GDC 17), Electrical Power Systems, of Appendix A, General Desien Criteria for Nuclear Power Plants, of 10 CFR 50.

2. General Design Criterion 5 (GDC 5), Sharing of Structures, Systems, and Components, of Appendix A, General Design Criteria for Nuclear Power Plants, of 10 CFR 50.

3. General Design Criterion 13 -(GDC 13), Instrumentation and Control, of Appendix A, General Design Criteria for Nuclear Power Plants, of 10 CFR 50.

4. IEEE Standard 308-1974, Class IE Power Systems for Nuclear Power Generating Stations.

5. Staff positions as detailed i.n a letter sent to the licensee, dated August 8, 1979.1

6. ANSI C84.1-1977, Voltage Ratings for Electric Powe- Systems and Equipment (60 Hz).

Six review positions have been established from the NRC analysis

. guidelines1 and the above-listed documents. These positions are stated in Section 5.

3. SYSTEM DESCRIPTION A single-line diagram of the AC electrical distribution system at TMI-1 is shown in Figure 1. The TMI-1 Class IE electrical distribution

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different 230 kV substation buses and provide the source of power for startup operation and shutdown requirements. Each of the unit auxiliary transformers has two isolated secondary windings, one at 6900 V and one at 4160 V. The 4160 V windings supply the Class IE distribution systems.

4. ANALYSIS DESCRIPTION 4.1 Desien/Oceration Chances The licensee submitted analyses2 ,3 based on the following proposed changes:

1. The taps on the auxiliary transformers (UAT 1A, UAT 1B) will be changed from 230 kV to 224.75 kV.

2. Trip functions will be removed from the 480 V bus relays.

3. Designated loads will be automatically tripped upon actuation of an engineered safeguards (ES) signal.

4. Installation of new first and second level undervoltage relays with new setpoints in place of existing electromagnetic-type relays.

5. Institute new procedures to preclude starting either a condensate or a condensate booster pump during the ES block loading sequence.

All of the described modifications and procedural changes will be completed prior to the next TMI-1 startup.

4.2 Analysis Conditions The following conditions were considered in the review:

1. The maximum voltage drop between the 4160 V and 480 V buses or motor control centers and the connected equipment is 0.02%

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(4160 V) and 1.0% ( 40 V). All voltages shown in this report are equipment termiral voltages expressed as percentages of the respective equipment nominal voltage.

2. Automatic tripping of Bus IN and designated loads upon ES actuation was assumed; manual load shedding was not.

4.3 Analysis Results f

Table I summarizes the comparison of the Class IE equipment voltaga ratings and the analyzed worst case terminal voltages for 4160 V, 480 V and lower voltage equipment.

TABLE 1. CLASS 1E EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE T,ERMINAL VOLTAGES (% OF NOMINAL VOLTAGE)

Maximum Minimum -

Analyzed Equiement Condition Rated Analyzed Rated Stcacy State Transient 4000 V Start -- --

80.1 --

81 Operate 1 *.0 110 90 92 --

460 V Motors Start -- --

75 --

77 a

Operate 110 111 86 87 --

480 V Starters Operate 110 106 82 84 --

Pickup -- --

75 --

75 Dropout -- --

55 --

75 Below 480 V 110 b 90 b b

a. All 460 V motors have a service factor of 1.15. Using this, the licensee has demonstrated, utilizing IEEE Standard 141-1976 and NEMA Standard MG1-12.42, that no thermal damage to the motor will occur.if the motor is continuously operated 14% below the nominal voltage with the

. ambient temperature below 40*C and motor loading at or below the nameplate rating.

b. No terminal voltages analyzed. All lower voltage Class IE. loads are supplied from regulated transformers capable of correcting a 15% variation on the input voltage.4,5,6 5

The licensee's analyses have determined that the worst-case steady-state low-voltage condition occurs.with the offsite grid at minimum voltage, one auxiliary transformer supplying maximum plant loads, and both ES trains with the largest ES load demand. Under these conditions, the analyzed minimum terminal voltages for equipment supplied by the Class 1E 4160 V and 480 V buses is 92% for the 4160 V buses and 87% for a 480 V motor control center. All other 480 V equipment has afgher voltages.

The worst-case low voltage transient condition occurs with the above load and grid voltage and the simultaneous manual restart of the condensate and booster pumps. The resulting equipment terminal voltages for Class IE equipment supplied by 4160 V bus ID and 480 V bus 1E are 81% and 77%,

respectively. The transient voltages will_ return to steady state values within ten seconds as the pump motors come up to full speed.

The analyses providad by the licensee have shown that maximum voltages of 110* and 111% will occur on the respective 4160 V and 480 V buses with a maximum grid voltage and a minimum load on the plant buses.

4.4 Analysis Verification The licensee submitted the results,of their analysis testing on May 15, 1980, and September 30, 1983. Th'e result; of the earlier testing were reported in Referenes 5 as follows:

Met-Ed had previsouly determined by measurements the actual worst case voltage drops between buses /MCCs and loads for 4160 and 480V bus loads. Therefore, Met-Ed's verifiction test was only conducted to

, verify the analyzed bus voltages.

The Met-Ed verification method required the measurement of the grid voltage and IE bus /MCC loads, phase angles, and voltages. Using the measured grid voltage and bus /MCC loading, all IE bus /MCC voltages were calculated using the analysis methods. The measured and calculated bus /MCC voltages were then compared.

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Met-Ed provided the test data and results of their test verification with their May 5, 1980, submittal. The 4160V buses were loaded over 3 0*. . However, during the tests only four 480V IE buses were loaded to 30% of their analyzed loading with all IE 450V buses /MCCs loaded less than 1%. The results of their voltage comparison indicate that the analysis voltages are within .4% of the measured voltages for all IE buses /MCCs.

The later test was performed on engineered safeguards power distribution channel A. Channel B, essentially identical, was not tested.

Bus IT, not included in either test, is part of Channel B. Therefore, the accuracy cf the voltage analysis for bus IT can be inferred by comparison with the results provided for Channel A.

l Voltage measurements and corresponding analyses were made for starting L and running the full engineered safeguards train. All Class 1E buses were

): loaded to above 68% of capacity. The test included motor-starting I transient conditions.

t The results from Reference 4 show that in three of the 21 comparisons, the recorded voltage was lower than the analyzed voltage. The worst case for this veas 1.1% less than the anal.yzed voltage. In one case there was no difference between measured and calculated voltages. In 17 of the 21 comparisons, the recorded voltage was higher than the analyzed voltage.

This conservatism was limited to 3.9% less than the recorded voltage. In all, 95% of the cases ~were within 3% of each other and 81% of the cases were within 2% of each other.

The results, as reported on May 15, 1980 and September 30, 1983, show consistancy. The difference reported between the measured and the analyzed voltages remained essentially the same for the different test conditions, t

5. EVALUATION Six review positions have been established from the 13 NRC analysis i 1

guidelines and the references listed in Section 2. Each review position 7

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-is stated below, followed by the evdluation of the licensee submittals.

The following evaluations are based on the completion of the changes in

..ction 4.1 and the analysis submitted on May 15, 1980.

Position 1--With the minimum expected offsite grid voltage and maximum load condition, each offsite source, in conjunction with the onsite distribution system, must be capable of starting and of continuously operating all Class 1E equipment within the equipment voltage rating.

As shoven in Table 1 and discussed in Section 4.2, the analyzed equipment terminal voltages for all Class IE equipment will be above the minimum voltage rating with the minimum offsite grid voltage and under all steady state and transient loading conditions.

Position 2--With the maximum expected offsite grid voltage and minimum load conditions, each offsite source and distribution system connection combination must be capable of continuously operating all Class IE equipment without exceeding the rated equipment voltage.

The licensee's analysis indicates that, with the grid maxima 4 and the plant load minimum, the voltage at the Class 1E 480 V buses and motor control centers will be less than 1% above the maximum allowable value for 460 V motors. Sir.ce the analysis was made with the plant in shutdown condition and no motors connected to the Class 1E buses, the voltages will be within the motor rating when accident conditions require the connection of Class 1E motors to the buses. The voltage for the buses and other Class 1E equipment will also be within their ratings. Therefore, the requirements as expressed in the above position are satisfied.

E Position 3--Loss of offsite power to either the redundant Class 1E distribution systems or the individual Class 1E buses, due to operation of voltage protection relays, must not occur when the offsite grid voltage is within expected voltage limits.

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_ _ _ _ _ _ _ = - - - - - _ - _ _ _ _ _ _ . _

J As shown in Table 2, the voltage protection relays will not separate the Class 1E buses from the offsite power sources during the analyzed starting transients or during maximum-load steady state conditions.

TABLE 2. COMPARISON OF ANALYZED VOLTAGES AND UNDERVOLTAGE RELAY SETPOINTS

.' (IN % OF NOMINAL VOLTAGE)

Minimum Analyzed Relay Setooint a

Relay Voltage Time Voltage Time to trio 4160 V loss of_ voltage relays 77.9 <10 sec. 57.7 1.5 sec. 4160 V~ degraded voltage relays 88.5 continuous 86.4 10 sec.

a. Licensee has determined, by analysis, the minimum equipment voltages with the offsite grid at the minimum expected voltage and the worst-case unit-and Class IE loads. The bus voltage at the relay location is slightly higher than the given equipment voltage.

Position 4--Test results should verify the accuracy of the voltage analyses supplied.

The licensee has shown the calculations to be an accurate representation of actual conditions of the Class 1E buses and loads.

Position 5--No evsnt or condition should result in simultaneous or consequential-loss of both required circuits from the offsite power network to the onsite distribution system.

zThe licensee has determined that there are no events or conditions which could result in simultaneous or consequential loss of both required o-- offsite circuits and, therefore, TMI-1 presedts no-violation of GDC 17 in this' regard.3 Position 6--As required by GDC 5, each offsite source shared between units in a multi-unit station must be capable of supplying adequate

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starting and operating voltage for all required Class 1E loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.

Three Mile Island is the location of two nuclear power generating stations, TMI-1 and TMI-2. Each unit is independently connected to offsite power sources and have no common electrical power interconnections between units. Therefo"e, Position 6 is not applicable to TMI-1.

6. CONCLUSIONS I have reviewed the licensee submittals and find that, upon completion of the changes included in Section 4.1, there will be reasonable assurance tnat:

1. Each offsite source, in conjunction with the onsite distribution systems, has the capacity and capability to start and operate all Class IE loads without exceeding the equipment voltage rating with the offsite power sources within expected limits. (This is contingent on each TMI-1 Class 1E 460 V motor being operated within its load rating and with an ambient temperature below 40*C.)

2. The licensee has determined that no potential exists for a simultaneous or consequential loss of both offsite electrical sources.

3. The test performed by the licensee verifies the accLracy of the analysis.

4. Loss of offsite power to the Class IE buses, due to operation of the voltage protection relays will not occur with the offsite grid within its expected limits.

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7. REFERENCES

1. NRC letter, William Gammill, to all power reactor licensees (except Humboldt Bay), " Adequacy of Station Electric Distribution Systems Voltages," August 8, 1979.

2. Metropolitan Edison Company (Met-Ed) letter, J. G. Herbein to W. P. Gammill, NRC, dated October 16, 1979.

3. Met-Ed letter with technical report entitled, "TMI-1 Electric Distribution System Voltages," Revision 1, to R. w. Reid, NRC, dated May 15, 1980.

4. General Public Utilities Nuclear Corporation letter, H. D. Hukill to the Office of Nuclear Reactor Regulation, NRC, " Degraded Grid Voltage Test," September 30, 1983, 5211-83-263.

5. EG&G Idaho, Inc., report Technical Evaluation Report, Adecuacy of Station Electrical Distribution Systems Voltaces. Inree Mile Island Nuclear Station Unit 1, E. W. Rocerts, Octocer 1980. Er4G-EA-5258.

6. Final Safety Analysis Report (FSAR) for TMI-1, Section 8.2,

" Electrical System Design."

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NRC aoRu 335 "' " "' ' '

U.S. NUCLEAR REGULATORY COMMIS$10N BIBLIOGRAPHIC DATA SHEET EGG-EA-6453 4 TITLE AND SueTITLE . 2. Iteeve aimes Adequacy of Station Electric Distribution System

3. RECIPIENT S ACCESSION NO.

Voltages, Three Mile Island Nuclear Station, Unit 1

7. AUTHORtSi 5. DATE REPORT COMPLE TED M ON TM l YEAR A. C. Udy December 1983 9 PERFORMING ORGANIZATION NAME AND MAILING ADDRESS (factuar tea Cooef DATE REPORT ISSUED MONTM lVEAR December 19R3 EG&G Idaho, Inc. . ft,,,,,,,,,,

Idaho Falls, ID 83415

8. (Leave Drank) 12 SPONSORING ORGANIZATION NAME AND HAlltNG A00RESS (factuar les Coorf , ,

Division of Licensina Office of Nuclear Reactor Reaulation 11. FIN NO.

U.S. Nuclear Regulatory Commission Washington, DC 20555 13 TYPE OF REPORT PE mico cove RED Isacsus<re casest ,

Technical Evaluation Report 15 SUPPLE 9ENTARY NOTES 14 (Lea e ormel

16. ABSTR ACT 000 svoros or sessJ This EG&G Idaho, Inc., report provides a review of the capacity and capability of the onsite distribution system at the Three Mile Island Nuclear Station, Unit 1, in conjunction with the offsite power sources, to automatically start and continuously operate all required safety loads.

i.

17. KEY WORDS AND DOCUMENT ANALYSIS 17a. DESCRIPTORS l

1 17e IDENTIFiE RS!OPEN. ENDED TERMS

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